Learn how to determine whether your horse is underweight and what feeding options are available for your hard keeper.

I have been approached many times in the past 15 years by owners of thin horses concerned about their charges. In some cases the owners were worried that well-meaning neighbors or even strangers would report their underweight horses to animal control officers. Many times these were simply owners of older or athletic horses with problems maintaining body weight. In this article we will explore some of the most commonly asked questions about how to manage "skinny" horses.

Is My Horse Too Thin?

Owners and managers should first learn to estimate their horses' weight and also how to score these animals' body condition on a scale of 1 to 9 (with 1 being emaciated and 9 obese, as detailed at TheHorse.com/18827 or this video). Because it can be difficult to notice a horse's weight changes if you are around him daily, Kristen Janicki, MS, PAS, of Mars Horsecare US, in Dalton, Ohio, recommends monitoring both body condition and weight on a weekly basis. Maintaining records can help you determine if a horse's weight fluctuates regularly, possibly with seasonal changes, or if his weight loss should be a cause for concern. For example, horses in the wild lose weight routinely through the winter months when feed is scarce and then gain weight in spring and summer when forage is more readily available. Some stallions also lose weight during breeding season, especially those that have a large book of mares.

Desired weight and body condition vary with a horse's "job." Thus, what is thin for one discipline might be ideal for another. For example, horses competing in racing, eventing, and endurance tend to be thinner than horses competing in dressage, pleasure, or hunter competition.

Feeding the Rescued or Malnourished Horse

Especially in current economic times, countless horses fall under the "rescued/starved/malnourished" category. Here in Kentucky, for instance, routine articles in the local paper tell of horses being seized from owners who believed they were doing a good thing by taking in "unwanted" horses, but just didn't have the knowledge or resources to care for the animals properly.

Kathleen Crandell, PhD, equine nutritionist for Kentucky Equine Research, says "Refeeding the starved horse is very tricky to start with and should best be done with the help of a veterinarian." Horses do not get to a starved state (a body condition score of 2 or less) overnight and will take months to put weight back on. Even once the horse is back to a "normal" body condition and weight, he might never be able to be more than a companion animal or pasture buddy, depending on the severity of the malnourishment (Kronfeld, 1993).

Anyone willing to take on the challenge of rehabilitating a starved horse must also realize that it is easy to "kill with kindness." As a horse's nutritional status declines his digestive system loses the ability to properly produce enzymes and maintain the healthy bacterial population needed to digest feeds. When feed is introduce too quickly, without the presence of these enzymes and bacteria, the feeds will not be digested properly, and the horse's system might go into a state of shock, possibly including heart, respiratory, or kidney failure three to five days later. This condition is commonly called "refeeding syndrome" and is related to increased insulin levels, which might pull minerals--such as phosphorus and magnesium--from circulating blood, causing an electrolyte imbalance.

Thus, any feeding and dietary changes should be made slowly to allow the starved horse's system time to adjust. The following are recommended steps in rehabilitating these horses:

1. Horses that are severely malnourished and have had no access to feed should initially be offered only water, salt, and good-quality mixed grass/legume hay for a minimum of 10 days. Offer hay first at 1 pound per 100 pounds of the horse's current body weight and increase slowly (over several weeks) to 1 pound per 100 pounds of expected body weight. Then increase to 2 pounds per 100 pounds of expected body weight. Measure changes in body weight so you can adjust the amount of hay accordingly.

2. Provide probiotics to help improve digestive tract health, especially in the cecum where most fiber is digested.

3. Vitamin supplements, especially those that will help promote immune function (A, C), bone health (D), and muscle tissue integrity (E), might be beneficial. Nutritionists might also recommend supplementing vitamin K and many of the B vitamins, which are produced in the healthy horse's cecum but might be lacking in a malnourished animal.

4. Offer a good-quality grain once the horse is eating 2 pounds of hay per 100 pounds of expected body weight. As with the hay, grain should be introduced slowly, and a common recommendation is to start with 1/2 pound a day and increase from there. Depending on the horse, the maximum amount offered will end up being 1/2-1% of body weight. Consult a veterinarian or equine nutritionist about recommended feeds for your area. Easily digested senior feeds are often recommended for these horses.

Ultimately, it is important to remember that any diet change should be made gradually so the body has time to adjust.

Janice Holland, PhD, PAS

Horses that are suffering from disease, or are otherwise unhealthy, might also lose weight. Often these horses are not feeling well enough to consume their normal daily rations, so they are losing weight because of insufficient calorie intake. A performance horse with ulcers is one example of a usually healthy animal that might lose his desire to eat. Just as you would if you weren't feeling well, horses with a fever or respiratory infection might not have much appetite. Anytime an owner notices a change in a horse's eating habits, especially an abrupt change, he or she should call a veterinarian to evaluate the animal.

Why are Some Horses "Hard Keepers"?

A variety of factors can affect a horse's ability to maintain body weight, and according to Kathleen Crandell, PhD, equine nutritionist with Kentucky Equine Research, it is important to determine what is causing the horse to either lose weight or not gain weight. "The goal is to determine if there is just a lack of sufficient calories or if there is a confounding factor that is keeping the horse from gaining," she says.

One of the most common reasons for weight loss is limited access to fresh water and good-quality feed. A horse that is not drinking will not eat, and it's crucial to remember that most horses will not eat poor-quality feeds such as moldy hay unless they are desperate.

Some horses that are considered "hot" tempered or excitable might also have problems maintaining body weight. In many cases these horses are perfectly healthy but will need to consume more calories than other horses of the same size.

A horse's age can also affect weight. Horses that are considered "geriatric" or that have acquired age-related health conditions might have a harder time maintaining body weight. Sometimes this is related to reduced digestive efficiency or dental problems such as missing teeth, or it can be a result of arthritis that makes it painful for a horse to walk to feed sources.

Still other older horses might lose their assertiveness around the hay feeder and get pushed away from available feed by younger, more aggressive pasturemates. Owners and managers of older horses should watch these individuals carefully and ensure they can access good-quality feeds.

In the hard keeper's case, "Prior to analyzing a horse's diet, I want to make sure that the horse is healthy, parasite-free, and doesn't have any dental problems," says Janicki. "Many health issues can cause a horse of go off feed and lose weight, so we want to rule that out first."

Problems such as internal parasite infection, chronic liver disease, kidney disease, and equine Cushing's disease are just a few disorders that can cause weight loss. Contact a veterinarian anytime a horse starts losing weight unexpectedly, as this could indicate an underlying health issue.

Also keep in mind that eating causes quite a bit of tooth wear, and uneven wear can make eating difficult or even painful for the horse. Therefore, it is important to have a veterinary dental practitioner check your horse's teeth once--if not twice--a year to see if they need to be filed.

Feeding Options

If you and/or your veterinarian have determined your horse is too thin, the next step is to decide what and how to feed the horse for weight gain. To this end the horse will need to consume higher-calorie feeds or larger rations of his current feed. Some feed manufacturers might list caloric content in megacalories (Mcal) per pound or kilogram of feed on the feed tag. But remember that all diets should start with good-quality forage provided as hay, pasture, or some alternative sources.

A good place to get an estimate of a horse's dietary needs is from calculations in the National Research Council's Nutrient Requirements of Horses (2007) or from extension publications. Keep in mind that an individual horse's requirements might vary from these estimates--and a horse's caloric requirements change depending on a variety of factors, such as level of work, age, pregnancy status, health status, environment, etc.--so working with a nutritionist and monitoring weight and body condition score are important for fine-tuning intake.

The forage you choose depends on what is affordable and available in your area. In general grass hays contain just under 1 Mcal per pound and legume hays slightly more. Most horses do well on a good-quality grass hay or a grass and legume mixture. Horses should consume a minimum of 1% of their body weight in forage on a dry matter basis to maintain a healthy digestive system. So, for example, a 1,000-pound horse should receive a minimum of 10 pounds of forage daily. Horses might consume 2-3% of their body weight in forage if it is the only feed that makes up the diet. If good-quality forage is not available, then offer alternatives such as hay cubes or haylage to help maintain digestive system health.

When a horse cannot maintain body weight on good-quality forage alone, then you might need to offer him concentrates, either as pellets or a sweet feed. The advantage of using these is they contain two to three times as many calories as forage. Cereal grains as well as most commercial concentrates contain 2-3 Mcal per pound.

When approached by clients about what to do with a hard keeper, most equine nutritionists, including Crandell, tailor recommendations to each horse's specific circumstances. "To increase calories I recommend improving the quality and/or quantity of the forage, if possible, and then work on getting the right type of concentrate for the horse," she explains.

Some horses still have difficulty maintaining weight even when consuming good-quality forage and a concentrate. For these horses an additional calorie source might be necessary. One of the most commonly used supplements is fat, usually in the form of oil. Horses often find fats palatable, especially those from grain sources such as corn, soybean, and rice bran. Introduce oils (or any dietary changes for that matter) gradually so as not to cause digestive disturbances such as diarrhea or steatorrhea (greasy, oily feces). Nutritionists commonly recommend starting with ¼ cup oil per feeding, and increasing the amount gradually. Most horses can consume about 1 cup per feeding without negative effects, as long as it is increased to this amount over about two weeks. Often the amount a horse will consume is limited by oil quality and how much the base feed can absorb, as most horses will not drink or lick excess oil out of a feed bucket. Some managers find fat supplements in a dry format easier to handle.

"Depending on the situation I might suggest some other high-calorie supplements like rice bran or oil," says Crandell. "Often I come across a horse that does not digest forage well, and for them I would recommend alfalfa pellets and/or something like beet pulp."

As long as the horse is healthy, adding weight is really a matter of increasing caloric intake. As with all dietary adjustments, consult with a veterinarian or equine nutritionist first.

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